It is known from previous designs of hybrid airbag inflators that proper time phasing in the flow of gases, is critical for achieving an optimum airbag inflation sequence and preventing injuries to the vehicle occupants. If the time phasing is too rapid, the occupants will be subject to injuries form the large deployment forces. If the time phasing is too slow, the airbag fails to attain full deployment in time to prevent injury to the occupants. It is also known that a controlled onset of gas flow rate followed by a controlled high rate phase of deployment is desired in the proper function of the inflator to address protection of the out of position passenger, particularly the standing child situated in the area in which the airbag is deployed. Various approaches in the prior art have not fully resolved this problem.
In the hybrid type of inflator, this is achieved by initially rupturing the closure disk containing the cold gas in the high pressure source, then providing a phased flow of the hot gas from the solid propellant gas generator a short time (millisecond time frame) later. Gas flow control is achieved by dimensional and spatial relationship between the nozzle, the manifold and the diffuser ports.
In the pyrotechnic type of inflators the variable flow can be achieved by shaping the geometry and the burn rates of the gas producing propellant grains to provide an initial low flow rate, followed by a higher final flow rate of gases to achieve the desired staging. In the pure stored cold gas inflator, the staging must be accomplished using variable sequentially opened flow restrictions. This is accomplished by using eroding nozzles or some mechanical means to change the nozzle geometry, resulting in mechanisms subject to the effects of the large magnitude impact forces before and during function. None of the above systems have attained the optimum level of flow control.
In order to achieve the required staging for the inflation of the airbag in hybrid type airbag, the prior art has involved a number of approaches, using a combination of explosive means combined with mechanisms to achieve the desired results. One such approach is disclosed in U.S. Pat. No. 5,226,561 in which an initial explosive charge propels a projectile through the seal disk releasing the cold gas, then a spring pin mechanism which provides a short delay actuates a gas generating means to supply the hot gas. Although this concept has a short delay which provides some initial ignition staging it fails to provide gas flow control throughout the remainder of the functional cycle. In a second approach shown in U.S. Pat. No. 5,242,194 a hollow piston rod with an attached circular cutter punctures the seal disk and subsequently conducts flame from the igniter through the hollow piston rod to initiate the propellant ignition material. No delay or gas flow staging is provided by this concept. In other approaches as shown in U.S. Pat. Nos. 3,895,821 and 5,257,819 the propellant is disposed outside the high pressure cold gas storage vessel and uses pressure from the propellant, through complex mechanical means to rupture the seal disk and mix the cold and hot gases. No delay or gas flow staging is provided by these concepts. U.S. Pat. No. 5,263,740 describes several arrangements of a detonator to rupture the pressure vessel seal and to ignite various internal gas or heat producing materials to augment the total gas flow. No delay or gas flow staging is provided by any of the concepts presented in this patent.
Prior art single nozzle designs cannot be effectively sized to control both the initial onset rate of gas flow and the subsequent higher flow rate required for airbag inflation. Most of these approaches involve relatively large masses of mechanical components that are subject to the vehicle impact loads upon impact. Their proper function is influenced by these unpredictable magnitude impact loads, resulting in variations of function and timing, and therefore the proper staging of the inflation process of the airbag.
This improved ignition train apparatus of this invention contains no large moving masses which are subject to the impact loading, but obtains the desired staging by means of the initial disk rupture by the high velocity gas and metallic particle stream from a standard high energy initiator, the subsequent delay sequencer and bypass nozzle system in the ignition train apparatus for the hot gas generator. Additional focusing of the high velocity gas and metallic particle stream may be achieved by adjusting the geometry of the initiator housing.